Magnetic tape is commonly used for storage of digital data. The magnetic tape is spooled on at least one reel in a cartridge that is insertable into a digital data transfer apparatus in which data can be written onto the tape and/or data can be read from the tape. Such data transfer apparatus, which may be referred to as a tape drive, typically includes one or more tape heads for one or both of reading and/or writing data from or to the tape head.
One format for data storage in a helical scan tape drive is Digital Data Storage (DDS). Various versions of DDS exist, but each version uses the same width tape in Digital Audio (DAT) cartridges, including DAT72 and DDS4. The tape width is approximately 4 mm. There is a demand for more and more data storage capacity. This has, to some extent, been met by improved reading and writing techniques that have allowed increased amounts of data to be stored, without changing the tape length or width. Additionally, the tape length has increased by making the tape thinner so that more tape can be packed into a cartridge. However, this has a practical limit. Ultimately, despite the improvement provided by the measures mentioned above, the storage capacity of a given size of tape has a limit.
One solution to the problem of data storage capacity is to increase the width of the tape. Of course, a greater width provides more storage area. However, since, conventionally, the cartridge loading devices and tape guide assemblies of tape drives are designed to interact with a particular size of cartridge/tape, if a tape drive is designed to use a wider tape (and consequently a larger size cartridge housing the tape), the end user is left with the problem that legacy format tape cartridges would not be usable with the tape drive and so it would be necessary to maintain more than one tape drive, or transfer existing stored data to the wider tape.
The Applicant has proposed tape drives designed to accept different width tapes so that the end user may be provided with a tape drive that can be used with narrower legacy format tapes and newer, wider, tapes. One problem that arises with such tape drives is that, where the tape drive utilises a rotary scanning system to read/write data from/to the tape, different wrap angles are required for different tape widths.
A rotary scanning system typically comprises a rotary scanning head (also known as a helical scan head). The rotary scanning head is usually in the form of a drum that has one or more head elements positioned on its cylindrical surface for performing read and/or write operations. During a loading process of a tape cartridge holding tape for use by the tape drive, a portion of the tape is deployed, or drawn from, the cartridge and wrapped around a portion of the cylindrical surface of the drum so that it can be read from or written to by the tape head. In use, the tape is moved longitudinally past the drum whilst the drum rotates about its axis of rotation. The drum typically rotates much faster than the speed of movement of the tape.
Data is placed on the tape in tracks that extend diagonally across the tape, typically at an angle of approximately 6° to the lengthways direction, or longitudinal axis, of the tape. The angle of the tracks is determined mainly by the tilt in the axis of the rotating drum relative to the orientation of the tape. The precise angle of the tracks is also determined by the relative speed of the movement of the tape and the rotational speed of the drum. However, due to practical limitations on the speed of the tape and the rotational speed of the drum, the effect of the variations of the tape and drum speeds on the track angle is small. Therefore, in order to extend the recorded track across most of the width of the tape, the wrap angle must be increased for the wider tape. This can be achieved by providing two tape guide assemblies together with respective tracks and drive mechanisms for the tape guide assemblies. One tape guide assembly is dedicated to the narrow tape and the other is dedicated to the wider tape. The tape guide assemblies draw the respective tapes from their cartridges to respective deployed positions that provide the required wrap angles